Self-assembly properties of a temperature- and salt-tolerant amphoteric hydrophobically associating polyacrylamide

Abstract

We prepared amphoteric hydrophobically associating polyacrylamides (AHAPAM) consisting mostly of hydrophilic polyacrylamide backbones, but also including the ionic hydrophobic monomer N,N-dimethyl octadeyl allyl ammonium chloride (DOAC) and the anionic monomer sodium 4-styrenesulfonate (SSS). The AHAPAM copolymer was prepared by carrying out aqueous solution polymerization. Macroscopic and microscopic self-assembly properties of AHAPAM in solution, as well as the effects of salt, temperature, and shearing on its association behavior were studied by carrying out viscosimetry, rheology, fluorescence spectroscopy (FS), and environmental scanning electron microscopy (ESEM) analyses. The results show that the association of the aqueous copolymer solutions were greatly affected by the concentration of the copolymer. The critical association concentration (CAC) of the AHAPAM solution was found to be 0.165 wt%, which was determined by carrying out viscometry and fluorescence spectroscopy experiments. Adding sodium chloride resulted in an increase in the apparent viscosity, which corresponded to the anti-polyelectrolyte solution behavior of AHAPAM. Meanwhile, intermolecular hydrophobic associations helped AHAPAM form a dynamic physically crosslinked network in its structure, conferring on AHAPAM strong heat- and shearing-resistance properties. The apparent viscosity of the 0.5 wt% copolymer solution was maintained at 92 mPa s at 140 °C and 170 s⁻¹ shearing for 1 h. FTIR and ¹H NMR spectra indicated the structure of the hydrophobically associating copolymers. And using the dilution extrapolation method, the intrinsic viscosity [η] of AHAPAM was shown to be 858.5 mL g⁻¹.